As a mold-producing method for producing a mold, such as a master mold or a core, by use of a binder, the self-hardening mold producing process has been known. In the field of engineering casting, and other fields around the central field, in particular, the organic self-hardening mold producing process has already been become a generally used mold producing process instead of the inorganic self-hardening mold producing process from the viewpoint of productivity, casting-quality, and safety and hygiene. As the organic self-hardening mold producing process, known is a mold producing process of hardening a binder containing a water-soluble phenol resin with an ester compound.
Patent Document 1 suggests a binder composition, for organic-ester-curing foundry sand, wherein a phenol compound monomer is incorporated into a water-soluble phenol resin in a specified proportion, whereby the bench life can be extended without lowering the final strength of the mold. In Patent Document 1, as examples of the organic ester, the following are described: cyclic ester compounds, such as lactones, and ester compounds derived from a carboxylic acid having a linear structure and an alcohol.
Patent Document 2 suggests a curing agent composition in which an organic ester having active carbon is incorporated, thereby making it possible to give a high mold strength, and further capture effectively formaldehyde generated in the production process. In the curing agent composition in Patent Document 2 also, a phenol compound monomer is incorporated in order to extend the bench life without lowering the final strength of the mold. Moreover, besides the active-carbon-having organic ester, an organic ester for curing the water-soluble phenol resin is also incorporated therein. The active-carbon-having organic ester, and the organic ester for curing the water-soluble phenol resin, which are described in Patent Document 2, are each an ester compound derived from a carboxylic acid having a linear structure and an alcohol, or a cyclic ester compound such as a lactone.